Question

Swing components are basic building blocks of an application. Swing toolkit has a wide range of various components, including buttons, check boxes, sliders, list boxes. Everything a programmer needs for his job. In this section of the tutorial, we will describe several useful components.

JList Component

JList is a component that displays a list of objects. It allows the user to select one or more items.

package com.zetcode;

import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.Font;
import java.awt.GraphicsEnvironment;

import javax.swing.BorderFactory;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JList;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.SwingUtilities;
import javax.swing.event.ListSelectionEvent;
import javax.swing.event.ListSelectionListener;


public class ListExample extends JFrame {

  private JLabel label;
  private JList list;


  public ListExample() {

    initUI();
  }

  private void initUI() {

    JPanel panel = new JPanel();
    panel.setLayout(new BorderLayout());
    panel.setBorder(BorderFactory.createEmptyBorder(20, 20, 20, 20));

    GraphicsEnvironment ge =
      GraphicsEnvironment.getLocalGraphicsEnvironment();

    String[] fonts = ge.getAvailableFontFamilyNames();

    list = new JList(fonts);
    list.addListSelectionListener(new ListSelectionListener() {
      @Override
      public void valueChanged(ListSelectionEvent e) {
        if (!e.getValueIsAdjusting()) {
          String name = (String) list.getSelectedValue();
          Font font = new Font(name, Font.PLAIN, 12);
          label.setFont(font);
        }
      }
    });

    JScrollPane pane = new JScrollPane();
    pane.getViewport().add(list);
    pane.setPreferredSize(new Dimension(250, 200));
    panel.add(pane);

    label = new JLabel("Aguirre, der Zorn Gottes");
    label.setFont(new Font("Serif", Font.PLAIN, 12));
    add(label, BorderLayout.SOUTH);

    add(panel);

    pack();
    setTitle("JList");
    setDefaultCloseOperation(EXIT_ON_CLOSE);
    setLocationRelativeTo(null);
  }

  public static void main(String[] args) {
    
    SwingUtilities.invokeLater(new Runnable() {
      @Override
      public void run() {
        ListExample ex = new ListExample();
        ex.setVisible(true);
      }
    });
  }
}

In our example, we will display a JList and JLabel components. The list component contains a list of all available font family names on our system. If we select an item from the list, the label will be displayed in a font, we have chosen.

GraphicsEnvironment ge = 
  GraphicsEnvironment.getLocalGraphicsEnvironment();

String[] fonts = ge.getAvailableFontFamilyNames();

Here we obtain all possible font family names on our system.

list = new JList(fonts);

We create a JList component.

public void valueChanged(ListSelectionEvent e) {
  if (!e.getValueIsAdjusting()) {

Events in list selection are grouped. We receive events for both selecting and deselecting. To filter only the selecting events, we use the getValueIsAdjusting() method.

String name = (String) list.getSelectedValue();
Font font = new Font(name, Font.PLAIN, 12);
label.setFont(font);

We get the selected item and set a new font for the label.

JScrollPane pane = new JScrollPane();
pane.getViewport().add(list);

JLabel component is not scrollable by default. We put the list into the JScrollPane to make it scrollable.

Figure: JList

JTextArea component

A JTextArea is a multiline text area that displays plain text. It is lightweight component for working with text. The component does not handle scrolling. For this task, we use JScrollPane component.

package com.zetcode;

import java.awt.BorderLayout;
import java.awt.Dimension;

import javax.swing.BorderFactory;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.SwingUtilities;

public class TextAreaExample extends JFrame {

  public TextAreaExample() {
    
    initUI();
  }

  private void initUI() {

    JPanel panel = new JPanel();
    panel.setLayout(new BorderLayout());
    panel.setBorder(BorderFactory.createEmptyBorder(20, 20, 20, 20));

    JScrollPane pane = new JScrollPane();
    JTextArea area = new JTextArea();

    area.setLineWrap(true);
    area.setWrapStyleWord(true);
    area.setBorder(BorderFactory.createEmptyBorder(8, 8, 8, 8));

    pane.getViewport().add(area);
    panel.add(pane);

    add(panel);

    setTitle("JTextArea");
    setSize(new Dimension(350, 300));
    setDefaultCloseOperation(EXIT_ON_CLOSE);
    setLocationRelativeTo(null);
  }

  public static void main(String[] args) {

    SwingUtilities.invokeLater(new Runnable() {
      @Override
      public void run() {
        TextAreaExample ex = new TextAreaExample();
        ex.setVisible(true);
      }
    });
  }
}

The example shows a simple JTextArea component.

JTextArea area = new JTextArea(); 

This is the constructor of the JTextArea component.

area.setLineWrap(true);

The setLineWrap() makes the lines wrapped if they are too long to fit the text area's width.

area.setWrapStyleWord(true);

Here we specify, how is line going to be wrapped. In our case, lines will be wrapped at word boundaries—white spaces.

area.setBorder(BorderFactory.createEmptyBorder(8, 8, 8, 8));

We put some border around the text in the component.

pane.getViewport().add(area);

To make the text scrollable, we put the JTextArea component into the JScrollPane component.

Figure: JTextAra

JTextPane component

JTextPane component is a more advanced component for working with text. The component can do some complex formatting operations over the text. It can display also HTML documents.

package com.zetcode;

import java.awt.BorderLayout;

import java.io.IOException;
import java.util.logging.Level;
import java.util.logging.Logger;

import javax.swing.BorderFactory;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTextPane;
import javax.swing.SwingUtilities;

public class TextPaneExample extends JFrame {

  JTextPane textPane;

  public TextPaneExample() {

    initUI();
  }

  private void initUI() {

    JPanel panel = new JPanel();
    panel.setLayout(new BorderLayout());
    panel.setBorder(BorderFactory.createEmptyBorder(20, 20, 20, 20));

    JScrollPane pane = new JScrollPane();
    textPane = new JTextPane();

    textPane.setContentType("text/html");
    textPane.setEditable(false);

    textPane.setBorder(BorderFactory.createEmptyBorder(8, 8, 8, 8));

    loadFile();

    pane.getViewport().add(textPane);
    panel.add(pane);

    add(panel);
    pack();

    setTitle("JTextPane");
    setDefaultCloseOperation(EXIT_ON_CLOSE);
    setLocationRelativeTo(null);
  }

  private void loadFile() {

    try {
      String cd = System.getProperty("user.dir") + "/";
      textPane.setPage("File:///" + cd + "test.html");
    } catch (IOException ex) {
      Logger.getLogger(TextPaneExample.class.getName()).log(Level.SEVERE,
          null, ex);
    }
  }

  public static void main(String[] args) {

    SwingUtilities.invokeLater(new Runnable() {
      @Override
      public void run() {
        TextPaneExample ex = new TextPaneExample();
        ex.setVisible(true);
      }
    });
  }
}

This is the HTML code that we are loading into the JTextPane component. The component does not handle scrolling.

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>A simple html document</title>
</head>
<body>

<h2>A simple html document</h2>


<p>
<b>JTextPane</b> can display HTML documents. 
</p>

<br>

<pre>
 JScrollPane pane = new JScrollPane();
 JTextPane textpane = new JTextPane(); 

 textpane.setContentType("text/html");
 textpane.setEditable(false);
</pre>

<br>
<small>The Java Swing tutorial, 2013</small>

</body>

</html>

In our example we show a JTextPane component and load a HTML document. Example shows formatting capabilities of the component.

JTextPane textpane = new JTextPane(); 

textpane.setContentType("text/html");
textpane.setEditable(false);

We create a JTextPane component, set the content of the component to be a HTML document and disable editing.

private void loadFile() {

  try {
    String cd = System.getProperty("user.dir") + "/";
    textPane.setPage("File:///" + cd + "test.html");
  } catch (IOException ex) {
    Logger.getLogger(TextPaneExample.class.getName()).log(Level.SEVERE,
        null, ex);
  }
}

Here we determine the current working directory of the user. We load a HTML document into the pane.

Figure: JTextPane

In this chapter, we have continued covering basic Swing components.